Direct production of steel from oxides of iron



R. D. PIKE Filed Aug. 9, 1951 DIRECT PRODUCTION OF STEEL FROM OXI-DES OFIRON sept. 22, 1953 Patented Sept. 22, 1953 UNITED lSTATES TENT OFFICEDIRECT PRODUCTION OF STEEL FROM OXIDES OF IRON 8 Claims.

This invention relating as indicated to the production of steel in anelectric arc or other suitable type of steel making step, fromcarburized iron produced by gaseous reduction of iron oxide, is moreparticularly directed to a method of making carburized, partiallyreduced, discrete particles of metallic iron, for subsequent use in themaking of steel in a furnace of the electric arc type.

The present invention is an improvement of my prior patent in the UnitedStates No, 2,501,189, issued March 21, 1950, entitled, Production ofMetallic Iron from Iron Oxides, but carries the invention of thatearlier patent, further in that the reduced Viron with its relativelysmall content of unreduced iron, will be cooled in the presence ofreducing gas containing CO, below 1000 F. to form carbon in the massWhile cooling in order to enable this carbon to act as a reducing `andnon-oxidizing agent for the residual iron oxide remaining after gaseousreduction, during the subsequent melting in the electric arc furnace orother suitable step for melting and steel making. In addition, thisinvention is an improvement of the process described in Pilot-PlantProduction of Steel from Sponge Iron, Bureau of Mines Report ofInvestigations 44:98, August 1949, wherein certain tests were made on avariety of sponge irons, using various` ores and methods to producesteel of commercial grades. In that report it was found that animprovement in the melting characteristics of briquetted sponge ironcould be achievd by mixing with the iron certain amounts of carbon andin some cases, lime. Under these conditions, the sponge iron pellets, orbriquettes, were found to be somewhat softer and more easily broken thanthose made without the addition of carbon, but they melted down veryrapidly in the electric are furnace with no tendency to stick together,or bridge-over in the furnace.

My present invention may employ similar equipment and some of theprocess steps of my earlier patent, 2,591,189, though somewhat modified,and in addition, deposits carbon from the cool reducing gas containingCO by cooling the charge with it below l000 F. At and below thistemperature, the carbon deposits according tothe formula This reactionis catalyzed by the unreduced iron K oxide which is present ,with thereduced iron.

When suiicient` carbonY` has been deposited,

other inert gases may be employed for cooling, which will notdepositcarbon in the above manner, nor will they re-oxidize the ironwhich has already been introduced. This charge of discrete particles ofcarburized, partially reduced, metallic iron is subsequently heated,preferably in the electric furnace, using any desired alloyingingredients, to produce a superior quality of electric furnace steel.

Certain of the gases, principally CO, arising from the substantiallycomplete reduction of the iron oxide in the discrete particles in thesteel making step, may be recirculated into the reducing gas used forinitial reduction of the iron oxide, to increase its content of CO, aswill be further described, and thus to modify the ratio of the CO in thereducing gas to the hydrogen content of such gas, making the net resultof the reaction of reduction more exothermic, thereby tending to preventlowering of temperature during reduction.

This present proposal is particularly applicable` for the making ofsteel where natural gas and iron ore are in close proximity to eachother. An example of this might be the making of steel from the ironores of the Mesabi Range with the natural gas from Alberta, Canada,though other sources of gas could, of course, be used. As a substitutefor the iron ore of the Mesabi Range, pelletized taconite concentratesform a suitable feed for my reduction and steel making process. As astill further example, this process could be used in connection with theiron ores of Venezuela and the sulphur and nitrogen-free natural gasfrom the Anaco area of that country.

It is accordingly an object of my present invention to produce steeldirectly from iron ores, such as magnetite or hematite, in a gaseousreduction process without fusion, followed by depositing carbon in thepartially reduced ore, and then effecting a further substantiallycomplete reduction with fusion in a steel making step.

It is a further object of my invention to reduce the fuel and powerrequirements for making steel and the costs incident thereto, byemploying a reducing gas, preferably made by reforming natural gas, inthe direct reduction of iron ore, followed by melting to make steel.

It is a further object of my invention to make possible the economicalrecovery of metals from isolated deposits of iron ore in those parts ofthe world wherein coal is not readily available but where largequantities of natural gas are available.

1t is a further object of my invention to reduce iron with any suitablereducing gas, such as coke-oven gas, and to produce steel directly fromsuch partially reduced iron ore and deposited carbon in an electricfurnace or other type of tute natural gas for coke in the production ofsteel from iron ore.

plates the provision of an iron oxide. burden of discrete particles on adowndraft"hearth"23, fof which a suicient number are:providedtovl allowthe continuous fdow of the hot reducinglreformed gas through the bed..flhese hearths @23, have provisions for conducting the products ofcombustion and reduction toanotherpart of thezsysn tern, Where thelspent reduction reformed Vgas *maybe replenished 4'for reuse forusedfas Ygas for combustion. At the-outset, 'the'burden-.in the lhearth 23 is"preheated tby' thenintro'duction of vgas of combustion and lair,:preferably insubstantially theoretically correct mixture'forcompletecombustion, and, after it .attains a'ternperature for reduction,butlbelow the'fusionftemperature of the burden, the gas fof Vcombustion.and air are turned off .and 'therefcrrned reducing gas, composed.principally Nof hydrogen :and carbon monoxide, is admitted.iThis'igasis conducted downwardly through the charge in which thehydrogen and carbon imonoxide :combine with the oxygen of i the ironoxide" tol form water and carbon dioxide. A partof .theL-spentreformedreducing gas is conducted to Pai'dehumidifying and decarbonating system,preferably 4`of `the amine type i2 0a, after being 'cooled 1 in coolerl5. This portion of ythe#circulatinggrgas,.after leavingga, hastbeenrestoredtofits :original 'reducing power and isv cold. `.'It:fgoesi-toilthe rgas VVholder h, `:from whence 1 itzis Withdrawn neededin line ell'to yinitially cooland .deposit `carbon in `the pellets,thatxisto carburize. Thesefsarnepellets learlier .have .been :reduced:in reduction vessels 23, `except for laxsmall residual amount nof irono-xide. l"llie'spent'vvarinzreducing gasiissuing frorn'the bottom :of.reduction .vessels 23 in line "il, is cooled'inacooler'lafandcthencejoins the main circulating stream fof:sp.ent .reformedreduction gas flowing-.1in the :line'l' ata point roughly correspondingvto i150 after ythe main stream gashas'passe'd through cooler '15. Fromthis point the `entire yflovvnf spent-.reformed 'reducing `gas flows'through line: l 5f intov gas holder ill, from which it is withdrawn`asfneededin. the balance of thefcirculation.

The main flow offspent reformed:reducingl gas leaving reduction vessels23 in line 42 during the period when the iron yoxide is beingvreduced,is at an average temperature-of-about 1825.F. and it is `economicallyadvisable to pass lthis gas through Waste heatbOiIersIILthus reducingthe temperature to aboutc800--F. before entering the cooler l5, Where`thejgas vis 'brought into contact `with cold water andthe temperaturereduced to about V100" F.,'.thus dehumidifying the gas and also'removingsomeCOZ. The CO2 gathered from the amine-system2a, vis usefully ernployed in circulation in gas reforming plants il, as Will be presentlydescribed.

A part of the spent reformed `reducing gas stored in gas holderl'l,:goes.directly:to `gas le 20 perature.

l forming plants il, via line I9, where it joins with the necessaryamount of fresh natural gas, steam and the CO2 just mentioned, to formreformed natural gas. Another portion of the gas from holder il isburned with the preheated air at about 5000 from preheater 22 furnishingthe products of combustion which supply the heat for carrying out thegas reforming reaction. An kother .portion ofthe gas from holder li is1o with ain'iurnishing gas of combustion which is mixed directly at i2with the reformed gas which 'leaves Il at about 1472 F., thus raisingthe teinperatureoffthe mixture of the reformed gas and theggas ofcombustion, to about 1650" F.

The balance of the gas from holder il is mixed with air at "'24 and thetheoretical mixture for combustion-.containing substantially no surplusO2, is fired in one of the vessels 23 in which the iron oxide is beingheated up to reduction tem- This temperature is preferably to about.2000F. asiama-ximum at top of bed '.to .compensate for the fact ythatthe mixed. re- ;iformed gas .is introduced vduring the reduction rcycle:at about 16-50 F.

The spent inertgas issuing .from that one of the'reduction'vessels sinwhich the iron oxide is :beingxheated-preparatory to reduction, passesthrough line 25 at anaverage temperature cf about 1260F- and togetherwith the similar gas l `usedzfor coo-ling thereducediron oxide, passes 5plied needed through line 50 tothat one of theivessels '23 in which nalcooling oi the reduced iron oxide is being carried out after preliminarycoolingand carburizing by the cold reducingigas fromholder v290. When'socooled,

40 thereduced iron oxide may be removed from the Areduction vesselandexposed to the atmosphere Without Vre--oxidation .Complete coolingmaybe.. carried outiloy using the gas from yholder .2106, but'itlisinore`economical to use only so 5 much of' this gasfor cooling that `will.deposit the desiredcarbon, Vcompleting the cooling with gas from.holder-:28.

,A portion of the gas of combustion from line :25 may-@be recirculatedto to suitably reduce the'temperature of combustion, .in orderto avoidlocal overheating of the charge :in vessels The iron oxide thus reducedin reduction vesn sels 23, has'had about 90% of its Fe reduced to themetallic state, and has had deposited in it and on it, enough carbon toprevent oxidation in the electric furnace and to elect reduction of theiron oxide'present, forming steel. This partially reduced and carburizedmetal now is placed in bin 52, whence it is supplied to electric furnace33 Where it is melted for substantially ccmpletereduction of the ironoxide and Where any desired alloying ingredients may be added. COproduced. by reduction of iron oxide With carbon in the electric-furnacemay .be introduced into G5 the main circulation of the mixed reformedreredlld and Ysemi-sintered charge aside with a bulldozer, or othersuitable equipment, the vessel is filled with fresh iron oxide andreturned to its original starting condition, ready for heating up.

I prefer to have available, seven reduction vessels 23, of which one isa spare, so as to at all times have a continuous stream of hot reformreducing gas circulating in the system. Each of these vessels may beproportioned in size so as to produce 45 tons metallic iron per cycle,so that the total production from six vessels per cycle is, 6 45:270tons, from which it may be inferred that the productive cycle of eachpan is 6,1/2 hours, if the output is to be 1,000 tons metallic Fe daily,that is,

Example- In citing this example, for convenience a start will be made atl 3, which is the mixed reformed hot reducing gas at 1650 F., whichenters that one of the Vessels 23 which is under reduction. The make-upof this gas follows:

TABLE 1 Analysis of gas at 13 Constituent:

CO2 percent volume-- 3.7 CO do 19.8 I-Iz do 57.1 N2 do 5.6 H2O do 13.8S. c. f.1 gas per ton metallic Fe, produced by gaseous reduction 179,000

Y 1 Standard cubic feet, s. c. f. at 60 F. and sea level.

The spent reformed gas at an average temperature of 1825 F. leaving thevessel 23, has the following analysis:

TABLE 2 Spent reformed gas Constituent CO2 percent volume 6.00 CO do17.55 H2 do 49.2 N2 do 5.60 H2O do 21.7 S. c. f./ton metallic Fe 179,000

The following is the analysis of the gas diverted from the maincirculation 'and passed through Vthe amine system 29a:

TABLE 3l Constituent: f

CO2 percent volume 7.67 CO do f 22.4 H2 d0 62.8 N2 d0 7.16 S. c. f./tonFe 60,700

The analysis of the gas after being treated by the amine step at 29a,which goes to the gas holder 29h, whence it is withdrawn through line 40to cool and carburize hot reduced iron oxide, is as follows:

TABLE 4 Constituent:

CO percent volume-- 24.2 H2 d0 6.8.0 N2 do V7.8

The analysis of the same gas, after passing 6 through the hot, partiallyreduced iron oxide, is as follows:

TABLE 5 Constituent:

CO2 percent volume-- 4.0 CO do 17.2 H2 do 70.8 N2 d0 8.0 S. c. f./ton Fe54,000

This latter gas rejoins the main stream at 15b and thence goes throughline I6 into gas holder Il. Its analysis is given in the followingtable:

TABLE 6 Constituent CO2 percent volume-- 6.19 CO do 20.25 H2 d0 66.00 N2d0 7.56 S. c. f./ton Fe 133,760

The surplus gas from the gas holder I1 remaining after all requirementsof combustion have been satisfied, amounts to 52,600 s. c. f./ton Fe.This gas goes directly to the gas reforming plant, where it is joined by20,900 s. c. f /ton Fe of natural gas, of the analysis given in thefollowing table:

TABLE 7 Analysis of natural gas Constituent: Per cent volume CH4 '78.8C21-Ie 12.0 N2 7.0 CO2 2.2

The analysis of the gas issuing from the gas reforming plants Il, isgiven in the following table:

TABLE 8 Constituent:

CO2 Per cent volume 3.2 CO do 21.2 H2 do 61.1 N2 do 1.4 H2O do 13.1 S.c. f./ton Fe 167,000

This gas is mixed with hot gas of combustion, giving the analysis ofmixed reformed reducing gas with which this example started.

The analysis of the gas in the inert gas circuit, used for cooling, isgiven in the following table:

TABLE 9 nConstituent: Per cent volume CO2 12.0 'N2 64.4

'This gas is inert to the reduced iron in the vessels 23, after thesameY has been precooled with the cold reducing gas from the gas holder29h. In the following table is given a rsum of the gas flows expressedas S. c. f. (standard cubic feet) per ton metallic iron produced bygaseous reduction:

7 The heat balance of the operation is givenv in the following table, inwhich table the debit tem for heat in the natural gas is given as thoughthere were no surplus of circulating/gas. of combustion andA this latterenters into .the balance as the rst'credititern:

TABLE I1" Btu. por Debit items: ton Fe Heat in natural gas 3l, 300, 000Exothcrrnic heat ofrcduction ef FcaOn 4G, 000 ExothermicA heat ofreaction, 2CO- CO2|C 754, 000

Total debit items 32, 100, 000

Credit items:

Surplus gas for combustion l2, 640, 000 Surplus waste heatv steam 8,860, 000 Heat of the reforming reaction, by diierenca. P, 430, 000Sensible heat, gusci-combustion 994, 000 Sensible heat extracted by thecooling Water from the spent cooling gas 2; 090,000 Sensible heatextracted lby the cooling water from,

spent mixed reform cd gas in cooler 715i 3; 680, 000

'lctal crc-dit itoms 32,100, 000

From this table it be stated that the net requirements oi P. t. u. inthe naturalV gas are 18,660,000 per ton Fe. In View ofthe very low costof natural gas in many localities, this reduces the eost'of fuel to: aVery small item',

The circulation of reducing gas for cooling and carburising from the gasholder 29h through the reduced iron oxide in the vessels 23, may belooked upon as a closed circuit which is superimposed upon the majorcirculation of gas, and in this closed circuit, because oi the action ofthe amine system 29a, the gas is fully reduced to its original reformedcondition and then after passing through the iron oxide for cooling andcarburizing, returns to the main circulation at i519. This has animportant eiiect in increasing. the average reducing power of the maincirculation of gas. The latter recirculates into the gas reformingplants li, but about 60% of it is used for combustion purposes, thegases of combustion iirrally being discarded through vents. This acts asa bleed from the circulation, and prevents any substantial pick-up inthe concentration of nitrogen and other inert gases of the atmosphere.

Ii the CO gas from the electric furnace 33 is not returned tothecirculation, the exothermic heat of the reaction in vessels 23 is`about 46,000 B. t. u. per ton Fe. if the CO from they electric furnaceis returned to the circulation, preferably at I3, into the mixedreformed reducing gas, the exothermic heat of the reaction in thevessels 23 willbe increased to about 64,000 B. t. u. per ton Fe.

l claim:

l. The process 'oi reducingY iron oxide without fusion combined with themaking of steel from the reduced oxide, which comprises passing a` hotreducing gas substantially free of hydrocarbon containing endothermicand exothermic cornponents, the latter being CO, through the oxide at atemperature between 1650-2000" F. to reduce the greater part of it tometallic iron by gaseous reduction, cooling the oxide thus reduced withsimilar relatively cool reducing gas by the reaction 2CO=CO2l-C, todeposit sufficient carbon for reducing the unreduced oxide; thencompleting cooling under non-oxidizing conditions, and substantiallynishing the reduction of said oxide in a steelrnaking step, with theproduction of steel.

2. The process of reducing iron oxide without fusion and the furtherreduction of said Yoxide in a steelrnalrng step for the production ofsteel,

'which comprises heating saidA oxide to a temperature lovvfer ythanV itsr melting' temperature, passing a; hot; reducingv gas at a temperaturebetween 16501-2000" F; containing" endothermic and exo thermiccomponents, the latter being CO, substantially'free from hydrocarbons,through a bed of particles of theyoxide to reduce the greater part. of`the oxide; by gaseousl reduction while maintaining theA ratio of theendothermic and exothermic components of the reducing gases so that thestepof reduction is exothermic, cooling said reduced oxide with asimilar relatively cool reducing gasto deposit: sufficient carbon in themass by the reaction of 2CO=CO2+C for the subsequent reduction in thesteelrnaking step, and then completing the coolingvv under non-exiwdizing conditions, and lastly reducing the residual iron oxide with thedeposited carbon while adding the necessary alloying ingredients in thesteehnaking step to produce steel.

3. The process of reducing iron ore without fusion combined with themaking of steel from the reducedl oxide which comprises the followingsteps: Heating.v the oxide tc a temperature suitable for rapid gaseousreduction Without fusion, passing the reducing gas, substantially freefrom hydrocarbons, at a temperature between 1650- 2000" F. through thebed to reduce a major portion of it to metallic iron, said reducing gasccntaining exothermic and endothermic components, including CO as partotthe. eXothermic gas and H2 as` apart ofthe endothermic gas, maintainingthe ratiooi the CO. and. H2, in thegas so that the exotherrnicv heat ofreduction by CO will exceed that of the endothermic heat oi reduction byHz, cooling the reduced oxide with relatively cool reducing gas similarto said: hot reducing gas, being substantially free from C02, at, thepoint of introduction to carb-urine and partially cool, further cooling:with cooling gas of combustion, and melting said oxide with the saiddeposited carbon in a steelmalring step to produce steel'.

4. The process ofy reducing iron oxide without fusion and the furtherreduction and melting of said oxide in a steelmaking step, whichcomprises placing the oxide in a gas permeable bed upon a gaspermeablesupport ina container, and` carryingyout the several stepsnecessary for reduction and for placing the reduced metal in arelatively cool condition, vsuitable for exposure to the air, separatelyand serially carrying out the following steps without movement of thecharge except in the last step for stcelrnaking; iirst, heating bydowndrait passage through the bed Vwith gas of combustionto. atemperature suitable for rapid gaseous reduction, diverting a portion ofthis gas after passing through the bed for use in the subsequent coolingstep;v second, passing a hot reducing gas at a temperature betweenl650-2000 F. through the bed' to effect reduction of the major portionof the oxide by gaseous reduction Without fusion, said hot reducing gascontaining endothermic. and excthermic components, the latter being CO;third, passing relatively cool reducing gas through the bed to cool itand to deposit sucient carbon for subsequent substantially completereduction of the remaining unreduced oxide in a, steelmaki-ng ,step bythe reaction 2CO=CO2+C'; fourth, completing. the cooling undernon-oxidizing conditions by passing aforesaid unheated gasxof combustionthrough the bed; fth, placing the reduced charge in a steelmaking stepandk replacing the charge with a fresh charge of oxide for repetition ofthe steps; and siXth completing the reduction of the ore inatstleelmaking step and drawing off the molten S ee 5. The process ofreducing iron oxide without fusion which comprises passing a hotreducing gas substantially free of hydrocarbon containing endothermicand exothermic components, the latter being CO, through the oxide at atemperature between 1650-2000c F. to reduce the greater part of it tometallic iron by gaseous reduction, cooling the oxide thus reduced withsimilar relatively cool reducing gas by the reaction to depositsufficient carbon for reducing the unreduced oxide; then completingcooling under non-oxidizing conditions.

6. The process of reducing iron oxide without fusion which comprisesheating said oxide to a temperature lower than its melting temperature,passing a hot reducing gas at a temperature between 1650-2000 F.,containing endotherrnic and exothermic components, the latter being CO,substantially free from hydrocarbons, through a bed of particles of theoxide to reduce the greater part of the oxide by gaseous reduction whilemaintaining the ratio of the endothermic and exothermic components, ofthe reducing gases so that the step of reduction is exothermic, coolingsaid reduced oxide with a similar relatively cool reducing gas todeposit suicient carbon in the mass by the reaction 2CO=CO2C` for thesubsequent reduction in the steelmaking step, and then completing thecooling under non-oxidizing conditions.

'7. The process of reducing iron ore without fusion which comprises thefollowing steps: Heating the oxide to a temperature suitable for rapidgaseous reduction without fusion, passing the reducing gas,substantially free from hydrocarbons, at a temperature .between1650-2000u F. through the bed to reduce a major portion of it tometallic iron, said reducing gas containing exothermic and endothermiccomponents, including CO as part of the exothermic gas and H2 as a partof the endothermic gas, maintaining the ratio of the CO and H2 in thegas so that the exothermic heat of reduction by CO will exceed that ofthe endothermic heat of reduction by Hz, cooling the reduced oxide withrelatively cool reducing gas similar to said hot reducing gas, beingsubstantially free from CO2 at the point of induction to carburize andpartially cool, and further cooling with cooling gas of combustion.

8. The process of reducing iron oxide without fusion, which comprisesplacing the oxide in a gas permeable bed upon a gas permeable support ina container, and carrying out the several steps necessary for reductionand for placing the reduced metal in a relatively cool condition,suitable for exposure to the air, separately and serially carrying outthe following steps without movement of the charge except in the laststep for steelmaking; rst, heating by downdraft passage through the bedwith gas of combustion to a temperature suitable for rapid gaseousreduction, diverting a portion of this gas after passing through the bedfor use in the subsequent cooling step; second, passing a hot reducinggas at a temperature between 1&50-2000" F. through the bed to eiectreduction of the major portion of the oxide by gaseous reduction Withoutfusion, said hot reducing gas containing endothermic and exothermiccomponents, the latter being CO; third, passing relatively cool reducinggas through the bed to cool it and to deposit suicient carbon forsubsequent substantially complete reduction of the remaining unreducedoxide in a steelmaking step by the reaction 2CO=CO2-]C; fourth,completing the cooling under non-oxidizing conditions by passingaforesaid unheated gas of combustion through the bed; and fth, replacingthe charge with a fresh charge of oxide for repetition of the steps.

ROBERT D. PIKE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,319,589 Jones Oct. 21, 1919 2,501,189 Pike Mar. 21, 1950FOREIGN PATENTS Number Country Date 238,270 Great Britain Aug. 14, 1935

1. THE PROCESS OF REDUCING IRON OXIDE WITHOUT FUSION COMBINED WITH THE MAKING OF STEEL FROM THE REDUCED OXIDE, WHICH COMPRISES PASSING A HOT REDUCING GAS SUBSTANTIALLY FREE OF HYDROCARBON CONTAINING ENDOTHERMIC AND EXOTHERMIC COMPONENTS, THE LATTER BEING CO, THROUGH THE OXIDE AT A TEMPERATURE BETWEEN 1650-2000* F. TO REDUCE THE GREATER PART OF IT TO METALLIC IRON BY GASEOUS REDUCTION, COOLING THE OXIDE THUS REDUCED WITH SIMILAR RELATIVELY COOL REDUCING GAS BY THE RERACTION 2CO=CO2+C, TO DEPOSIT SUFFICIENT CARBON FOR REDUCING THE UNREDUCED OXIDE; THEN COMPLETING COOLING UNDER NON-OXIDIZING CONDITIONS, AND SUBSTANTIALLY FINISHING THE REDUCTION OF SAID OXIDE IN A STEELMAKING STEP, WITH THE PRODUCTION OF STEEL. 